Ocean bottom node (OBN) seismic data are acquired using a group of nodes, which are autonomous units, that are placed at locations on the sea floor to record and store the full seismic wave-field (pressure and shear) resulting from a number of shots provided along a shot line or series of shot lines at or near the surface of the water. In order to obtain the full seismic wave-field data, each node is currently physically retrieved, and the stored data are downloaded for evaluation. Future technical developments may permit remote data transfer negating the need to physically retrieve the node until operationally warranted. Current methods for acquiring and analyzing the data result in inaccuracies in the known position of the node, in particular for deep water seismic surveys, and the timing of the recorded data. Such inaccuracies include the node geographical position (X, Y & Z), time errors related to the internal clock within each node and environmental aspects such as time distortion due to water column and tidal variations within the duration of the survey.
Accurate determination of node location is important in analyzing the recorded seismic data. Typically, node position is initially identified using satellite or interferometric methods generally related to the ship and remotely operated vehicle (ROV) used to deploy each node. An autonomous underwater vehicle (AUV) may be employed in place of an ROV. This may be supported by similar identification of node position when each node is recovered. These typical methods are prone to inaccuracies. In addition, as nodes are autonomous units, each node has an internal clock to describe chronological time. However, these internal clocks do not keep time to the degree of accuracy required for seismic data and often drift from the true time. Since each node has an individual clock, this clock drift varies from node to node. Resolving inaccuracies in the fidelity of the on-board clock or other factors that relate to accurate timing of the data is important in processing node data. Unfortunately, these various factors that cause timing infidelity may interact in a non-linear manner, causing problems in resolving one from the other.
An existing method for determining node position errors in deeper water relies on time-slices through the direct arrival times describing circles around the node location. With knowledge of the shot locations that contribute to the node, the coordinates of the center of all such circles around nodes' location can be calculated. These circle centers generate a probability function with statistical parameterization that defines the location of each node. Other existing methods include simultaneous inversion using single value decomposition for node position, clock drift and water velocity as described in Docherty, P. and Hays, D., Ambiguities in direct arrival time inversion for ocean bottom nodes, 74th EAGE conference and exhibition, (2012) and a method of mapping direct arrival times of adjacent nodes to the same time. The results of these existing methods for determining node position errors can be influenced by other errors, particularly timing errors due to clock-drift. Conversely, methods for determining the clock-drift suffer in the presence of node position errors negating the ability to satisfactorily resolve one or the other. Therefore, improved methods for determining node positioning errors from recorded seismic data even in the presence of clock drift are desired.